Controllable self-assembly of a mesomeric metallo-organic helicate and its π-electron number dependent encapsulation of polycyclic aromatic hydrocarbons (PAHs)

Abstract

In the field of metallo-organic helicates, the controlled synthesis of low-symmetric structures remains a significant challenge due to the need for the precise control over the self-assembly process due to their thermodynamically disfavored nature, compared to highly symmetric forms. This study introduces an effective strategy by shifting the design focus from ligands to metal centers. Through precise regulation of the stereoconfiguration, two metal centers are directed to adopt opposite handedness, affording a mesomeric and C₁ symmetric helicate structure S, fully characterized by ¹H NMR, ESI-MS and SC-XRD analyses. The resulting helicate structure features a well-defined square cavity with an 8.5 Å distance between the roof and the floor, capable of accommodating planar polycyclic aromatic hydrocarbons (PAHs) via π–π stacking interactions within the optimal range after slight compression. More importantly, the binding constants show a proportional enhancement with the increase in the number of π-electrons and π-areas in PAH guests. This work points toward a new direction for developing functional low-symmetric metallo-organic supramolecular assemblies. In addition, the clear structure–function relationship highlights their potential applications in molecular separation and sensing.